For some time, cords which are used on telephone instruments to connect a handset to a base or housing have been formed in a retractile configuration and have come to be known as spring cords. Such cords must have sufficient retractility to insure that they will return rapidly to their normal retracted form after having been extended and released and at the same time be sufficiently extensible so that they are capable of being extended without the application of excessively high forces.
Spring cords are generally constructed of highly flexible cordage having a plurality of individually insulated, mandrelated tinsel conductors. Each of these conductors is made by wrapping a plurality of tinsel ribbons made of a Phosphor-bronze material spirally around a multi-filament nylon center core. In the past, a retractile cord was made by enclosing the conductors in a braid comprising cotton and plastic strands and by enclosing the braid in an outer jacket of vulcanized rubber. See for example, U.S. Pat. No. 2,573,439 which issued on Oct. 30, 1951 in the name of G. E. Henning. More recently, each tinsel conductor has been covered with a served, knitted nylon and then insulated with an extrudable, plasticized polyvinyl chloride (PVC) composition after which the plurality of individually insulated conductors were jacketed with a plasticized PVC composition. See for example, U.S. Pat. No. 3,037,068. Cordage which was made by the just-described method was formed into spring cords in a manner such as described in U.S. Pat. Nos. 2,920,351 and 3,024,497 which issued on Jan. 12, 1960 and on Mar. 13, 1962, respectively, in the names of E. C. Hardesty and D. L. Myers, and which are incorporated by reference hereinto.
This construction proved to be necessary because of stringent service requirements that have been placed on telephone cords. The served tinsel conductor construction provided a high degree of cut-through protection for the PVC jacket during flexing, and the PVC jacket compound provided a protective outer jacket and maintained the arrangement of the individual conductors in a circular configuration. The above-described cordage design was determined to be suitable for the production of (1) a flexible straight or line cord which connects the telephone housing to a wall terminal and (2) a retractile cord which connects the handset to the telephone housing.
A new concept in telephone station equipment includes the termination of a length of telephone cordage with a modular plug instead of individual spade-tipped conductors to provide what has come to be known as a modular cord. Jacks adapted to receive the plugs are mounted in the telephone housing or base and in a wall terminal thereby permitting easy replacement of either the line or spring cord by a customer or an installer. For a description of modular plugs and jacks, see for example, U.S. Pat. Nos. 3,699,498 and 3,761,869 which issued Oct. 17, 1972 and Sept. 25, 1973, respectively in the names of E. C. Hardesty, C. L. Krumreich, A. E. Mulberger, Jr. and S. W. Walden, and U.S. Pat. No. 3,860,316 which issued Jan. 14, 1975 in the name of E. C. Hardesty, all incorporated by reference hereinto.
Conversion to modularity and its associated plug-terminated cordage necessitated the development of telephone cordage having a smaller cross-section than that used in the past. A cordage design suitable for use with the modular plugs incorporated smaller conductors arranged in a parallel, planar array and enclosed with a somewhat oval-shaped jacket.
The dimensional constraints imposed by the modular plugs and jacks necessitated a reduction in the overall size of both the insulated conductors and of the jacket of the cordage. To reduce the size of the insulated conductor, it was necessary to replace the protective knitted nylon covering over the served tinsel with an insulation which would function as a high strength barrier to the cutting action of the tinsel conductors, and as the primary component to achieve resiliency in a retractile telephoe cord. The presently used modular cord includes conductors which are insulated with a polyethylene polyester thermoplastic copolymer such as is described in U.S. Pat. No. 4,090,763 which issued on May 23, 1978 in the names of W. I. Congdon et al, and which is incorporated by reference hereinto.
While such modular cords are suitable for many of the telephone instruments now on the market, customer reaction has mandated a new design for at least one style of a decorative telephone series. One such example is a decorative telephone which is sold under the designation Country Junction*, a trademark of the American Telephone and Telegraph Company. The Country Junction telephone includes a wooden cabinet that resembles an instrument used at the beginning of the century and which also includes a pair of pewter nonfunctional ringers. Market studies have shown that a telephone cord having a braided outer jacket is compatible with the Country Junction telephone and results in an attractively styled piece of customer station equipment.
The choice of a cord having a braided outer jacket for this particular telephone presents a problem. The cord which is presently supplied with the Country Junction telephone is a relatively short line cord which comprises a plurality of conductors individually enclosed in a nylon knit and a PVC cover with the plurality enclosed in a braided covering. Each end of the cord is whipped with thread to prevent fraying of the braided covering when the cord is terminated. Not only is such a cord not conducive to being formed into a retractile cord because of its lack of a memory element, but it is relatively expensive to terminate. Also, the braid is incapable of performing one function of the plastic jacket in a conventional modular cord, that function being to maintain the conductors in an ordered array at an end portion of the cord to facilitate their entry into correct ones of conductor-receiving troughs in a modular plug. Further, the shortened cord between the handset and the wall-mounted base severely limits the use of the telephone, particularly in a kitchen environment where it most usually will be installed. On the other hand, the use of a lengthy straight cord between the handset and the base would be a return to the problem of a dangling cord which was overcome by spring cords.
The above-described cords having a braided outer jacket have not been made into a retractile configuration to connect the handset to the wall cabinet of the Country Junction telephone because to do so would require the dispersal of rubber strands among the individually insulated conductors to provide the memory capability for the cord. See for example, U.S. Pat. No. 2,136,743. While the rubber strands provide memory for the cord so that it can be made into a retractile configuration, the arrangement of the strands and the conductors is relatively expensive to braid. Moreover the resultant cord cross-section, particularly at the whipped ends, is too large for use with modular plugs such as those disclosed in the above-identified Hardesty U.S. Pat. No. 3,860,316 which are used to terminate the end portions of the cords.
The prior art appears to be of little help in overcoming this problem. Straight cords having braided outer jackets have been used, plastic cords are now used--but the problem is to market a telephone which emulates the past but is compatible with present day modularity. Clearly, there is a need to provide a retractile telephone cord which may be terminated with modular plugs and which is capable of having a braided outer covering that is compatible with the telephone instrument to which it is connected.